MAGNITUDE AND TIME-COURSE OF ACUTE HYPOXIC PULMONARY VASOCONSTRICTIONIN MAN

Acute hypoxic pulmonary vasoconstriction has an established role in th e preservation of ventilation-perfusion balance. To further characteri ze this homeostatic response in man we have attempted to measure both the time course and magnitude of blood flow diversion from single hypo xic lobes. Lobar hypoxia (mean P-O2 38 +/- 1.5(SEM)mmHg, mean P-CO2 39 .9 +/- 0.9 mmHg) was induced by inflating catheter-tip balloons in lef t upper lobe bronchi during fibreoptic bronchoscopy under local anaest hesia in 8 normal subjects. An index of lobar blood flow was obtained by acquiring dynamic scintigraphic lung images during a continuous int ravenous infusion of the short-lived radioisotope krypton-81m dissolve d in 5% glucose solution. In 3 subjects blood flow to the occluded lob es was monitored while the lobes were maintained under hyperoxic condi tions (mean P-O2 127.8 +/- 31.5 mmHg, mean P-CO2 40.2 +/- 1.3 mmHg). U nder hypoxic conditions the blood flow to the occluded lobes fell to 5 3% of baseline after 5 min with a mean time constant of 151 +/- 24.8 s ec. Under hyperoxic conditions there was no significant change from ba seline blood flow. We conclude that this technique has allowed us to m onitor both the dynamic and steady state responses of the pulmonary ci rculation to lobar hypoxia in man.